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09QUV & Q-SUNA Comparison of Two Effective Approaches to Accelerated Weathering & Light Stability Testing
The Need For TestingLight, high temperature, and moisture, can cause damage to coatings, plastics, inks, and other organic materials. The resulting damage can be seen in many different types of polymerdegradation. These include changes in physical properties such as cracking, peeling, embrittlement,loss of tensile strength, etc; as well as visual properties such as gloss loss, fading, yellowing, colorfade and color change.
For many manufacturers, it is crucial to formulate products that can withstand weathering and light expo-sure. Accelerated weathering and light stability testers are widely used for research and development, quality control and material certification. These testers provide fast and reproducible results.
Two Different ApproachesIn recent years, low-cost and easy to use laboratory testers have been developed, including the QUV® Accelerated Weathering Tester (ASTM G154) and the Q-SUN® Xenon Test Chamber (ASTM G155).
This paper will explore the ways in which these two testers differ, including emission spectra and method of moisture simulation. The inherent strengths and weaknesses of each tester will be discussed, including purchase price and operating costs. Guidelines will be given for which tester is generally recommended for a particular material or application.
The QUV tester is the world's most widely used weathering tester. It is based on the concept that, for durable materials, short-wave UV causes most weathering damage.
Q-SUN Xenon Test Chambers reproduce the full spectrum of sunlight, including ultraviolet, visible light and infrared.
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Historical PerspectiveWhile it is clear that weatherability and light stability are important for many products, the best way to test is sometimes controversial. Various methods have been used over the years. Most researchers now use natural exposure testing, the QUV Weathering Tester, or a xenon arc chamber, such as the Q-SUN Xenon Test Chamber. Natural exposure testing has many advantages: it is realistic, inexpensive and easy to perform. However, many manufacturers do not have several years to wait and see if a “new and improved” product formulation is truly an improvement.
The Q-SUN (xenon arc) and QUV (fluorescent UV) are the most commonly used accelerated weathering testers. The two testers are based on completely different approaches. The xenon test chamber reproduces the entire spectrum of sunlight, including ultraviolet (UV), visible light, and infrared (IR). The xenon arc is essentially an attempt to simulate sunlight itself, from 295 nm - 800 nm (see Figure 1 below).
The sunlight spectrum consists of various wave-lengths, which determine a material's mode of degradation in an outdoor environment.
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The QUV Accelerated Weathering Tester, on the other hand, does not attempt to reproduce sunlight, just the damaging effects of sunlight that can occur from 300 nm - 400 nm. It is based on the concept that, for durable materials exposed outdoors, short-wave UV causes the most weathering damage (Figure 1).
Which is the better way to test? There is no simple answer to this question. Depending on your appli-cation, either approach can be quite effective. Your choice of tester should depend on the product or material you are testing, the end-use application, the degradation mode with which you are concerned, and your budgetary restrictions.
To understand the differences between the Q-SUN and the QUV testers, it is necessary to first look more closely at why materials degrade.
Sunlight compared to the QUV and the Q-SUN testers. The QUV weathering tester provides the best available simulation of sunlight in the short-wave UV region from 365 nm down to the solar cut-off. How-ever, it is deficient in longer wavelengths. The Q-SUN chamber reproduces sunlight's full spectrum, which is critical for testing many products that are sensi-tive to long-wave UV, visible light, and infrared.
Figure 1- Q-SUN and QUV Testers vs Sunlight
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Moisture. Dew, rain, and high humidity are the main causes of moisture damage. Our research shows that objects stay wet outdoors for a surprisingly long amount of time each day (8-12 hours daily, on average). Studies have shown that condensation, in the form of dew, is responsible for most outdoor wetness. Dew is more damaging than rain because it remains on the material for a long time, allowing significant moisture absorption.
Of course, rain can also be very damaging to some materials. Rain can cause thermal shock, a phenomenon that occurs, for example, when the heat that builds up in an automobile over the course of a hot summer day is rapidly dissipated by a sudden shower. Mechanical erosion is caused by the scrubbing action of rain. This can also degrade materials such as wood coatings. Because rain wears away the surface, fresh material is continually exposed to the damaging effects of sunlight.
The major effect of humidity on indoor materials is often the physical stress caused by the mate-rial trying to maintain moisture equilibrium with its surroundings. The greater the range of humidity the material is exposed to, the greater the overall stress. Although indoor products, such as textiles and inks, may only be exposed to moisture in the form of humidity, it can also be an important factor in the degradation of outdoor materials. Outdoors, the ambient relative humidity (RH) will affect the speed at which a wet material dries.
The QUV and the Q-SUN testers each reproduce light, temperature, and moisture in different ways.
Dew, not rain, is responsible for most of the damage caused by outdoor wetness.
Products exposed outdoors often remain wet 8-12 hours each day.
Both sunlight through window glass and bright indoor lighting can degrade some materials.
Triple Threat: Light, Temperature, and MoistureMost weathering damage is caused by three factors: light, high temperature, and moisture. Any one of these factors may cause deterioration. Together, they often work synergistically to cause more dam-age than any one factor alone.
Light. Spectral sensitivity varies from material to material. For durable materials, like most coatings and plastics, short-wave UV is the cause of most polymer degradation. However, for less durable materials, such as some pigments and dyes, longer wave UV and even visible light can cause significant damage.
High Temperature. The destructive effects of light exposure are typically accelerated when temperature is increased. Although temperature does not affect the primary photochemical reaction, it does affect secondary reactions involving the by-products of the primary photon/electron collision. A laboratory weathering test must provide accurate control of temperature, and it usually should provide a means to elevate the temperature to produce acceleration.
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QUV Weathering TesterSunlight Simulation. The QUV is designed to reproduce the damaging effects of sunlight on durable materials using fluorescent UV lamps. These lamps are electrically similar to the common cool white lamps used in general lighting, but are designed to produce mainly UV rather than visible light or infrared.
There are different types of lamps with different spectra. The type of lamp should best resemble the light conditions found in your end use environ-ment. UVA-340 lamps provide the best available simulation of sunlight in the critical short-wave UV region. The spectral power distribution (SPD) of the UVA-340 matches sunlight very closely from the solar cut-off to about 360 nm (Figure 2). UV-B lamps (Figure 3) are also commonly used in the QUV. They typically cause faster degradation than UV-A lamps, but their short wavelength output below the solar cut-off can cause unrealistic results for many materials.
UVA-340 lamps provide the best available simulation of sunlight in the critical short-wave UV region.
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UV-B lamps utilize short-wave UV for maximum acceleration and are most useful for testing very durable materials, or for quality control.
1 The SOLAR EYE Irradiance Controller is used in models QUV/se and QUV/spray. The SOLAR EYE controller allows better reproducibility and repeatability than the manual irradiance control procedure used for the model QUV/basic. The SOLAR EYE controller also reduces maintenance because the lamps do not have to be rotated and replacement of lamps is less frequent.
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The QUV Accelerated Weathering Tester uses fluorescent UV lamps to reproduce the damaging effects of sunlight on durable materials.
In just a few days or weeks, the QUV can reproduce the damage that occurs over months or years outdoors.
Control of Irradiance. Control of irradiance (light intensity) is necessary to achieve accurate and reproducible test results. Most QUV models are equipped with the SOLAR EYE® Irradiance Con-troller.1 This precision light control system allows the user to choose the level of irradiance. With the SOLAR EYE controller's feedback-loop system, the irradiance is continuously and automatically monitored and precisely maintained. The Solar Eye automatically compensates for lamp aging or any other variability by adjusting power to the lamps. Figure 4 shows how the irradiance control system works.
Figure 2 - Noon Summer Sunlightvs UVA-340 Irradiance
Figure 3 - Sunlight, UVB-313, and FS-40
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Figure 4 - QUV Weathering Tester Irradiance Control
QUV SOLAR EYE Irradiance ControllerWith the SOLAR EYE controller's automatic feed-back loop system, the irradiance is continuously monitored and precisely maintained.
How it Works
Step 1: The operator selects the desired irradiance level. The level selected is the “set point.”
Step 2: During the UV cycle, built-in sensors measure the light from each pair of lamps and transmit this data to the controller.
Step 3: Both the set point and the actual irradiance are continuously displayed for each pair of lamps.
Step 4: The controller compares the measured irradiance to the set point.
Step 5: Then the controller instructs the power supply to adjust the voltage to the lamps to main-tain the set point.
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The QUV tester with the SOLAR EYE Irradiance Controller provides better lamp life and better reproducibility and repeatability than testers with manual irradiance control. Maintenance is simplified because lamps do not have to be rotated.
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QUV Weathering Tester cont.
In the QUV weathering tester, control of irradiance is simplified by the inherent spectral stability of its fluorescent UV lamps. All light sources decline in output as they age. However, unlike most other lamp types, fluorescent lamps experience no shift in spectral power distribution over time. This enhances the reproducibility of test results and is a major advantage of testing with QUV machine.
Figure 5 shows a comparison between a lamp aged for 2 hours and a lamp aged for 5600 hours in a QUV model with irradiance control. The difference in output between the new and aged lamps is nearly indistinguishable. The SOLAR EYE Irradiance Con-troller has maintained the light intensity. In addition, due to the inherent spectral stability of fluorescent lamps, the spectral power distribution remains vir-tually unchanged. The same data is graphed as a percentage difference in Figure 6.
In addition to its other advantages, the patented SOLAR EYE system allows for easy calibration, NIST traceability and ISO compliance.
While all light sources decline in output as they age, the QUV tester's SOLAR EYE control system keeps the irradiance at a consistent level by adjusting the power to the lamps.
The QUV tester's spectrum changes very little be-cause of the inherent spectral stability of fluorescent lamps.
With the patented AUTO CAL® system and the
CR10®, calibration takes only minutes, is NIST traceable and complies with ISO 9000 requirements.
The CR10 Radiometer should be returned annually to Q-Lab's A2LA accredited lab for ISO 17025 compliant recalibration.
Figure 5 - QUV Tester Lamp Aging
Figure 6 - % Difference in AgedQUV Tester Lamps
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Because materials experience such long wet times outdoors, the typical QUV unit's condensa-tion cycle is at least 4 hours. Furthermore, the condensation is conducted at an elevated tem-perature (typically 50˚C). This greatly accelerates moisture attack. The QUV tester’s long, hot con-densation cycle reproduces the outdoor moisture phenomenon far better than other methods such as water spray, immersion, or high humidity.
In addition to the standard condensation mecha-nism, the QUV tester can also be fitted with a water spray system to simulate other damaging end-use conditions, such as thermal shock or mechanical erosion. The user can program the QUV weather-ing tester to produce cycles of wetness alternating with UV, a situation that closely correlates to natural weathering.
QUV Tester Moisture Simulation. A major benefit of using the QUV accelerated weathering tester is that it allows the most realistic simula-tion of outdoor moisture attack. Outdoors, ma-terials are frequently wet up to 12 hours a day. Because most of this moisture is the result of dew, the QUV machine uses a unique condensa-tion mechanism to reproduce outdoor moisture.
During the QUV tester's condensation cycle, a water reservoir in the bottom of the test chamber is heated to produce vapor. The hot vapor main-tains the chamber environment at 100% relative humidity, at an elevated temperature. The QUV unit is designed so that the test spec-imens actual ly form the s idewal l of the chamber. Thus, the reverse side of the specimens is exposed to ambient room air. Room air-cooling causes the test surface to drop a few degrees below the vapor temperature. This temperature difference causes liquid water to continually condense on the test surface throughout the con-densation cycle. (Figure 7).
The resulting condensate is naturally distilled, pure water. This pure water increases the reproducibility of test results, precludes water-spotting problems and simplifies the QUV tester's installation and operation.
Optional water spray is particularly useful for roofing materials and coatings used on wood.
The QUV tester simulates outdoor moisture attack through a realistic, hot condensation system.
Room Air Cooling
Spray NozzleTest Specimen
UV Lamps
Swing-Up Door
Oxygenation Vent
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QUV Cross Section During Condensation Period
Figure 7 - QUV Accelerated Weathering Tester Cross Section During Condensation Period
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Q-SUN Xenon Test ChamberSunlight Simulation. Xenon arc testers are considered the best simulation of full-spectrum sunlight because they produce UV, visible light and infrared energy. Two examples of xenon arc testers are the full size Q-SUN Xe-3 and the table top Xe-1 (see Figures 8 and 9). Understanding xenon arc spectra is complicated by two factors: optical filter systems and lamp stability. Xenon arc lamps must be filtered to reduce unwanted radiation. Several types of glass filters are available to achieve various spectra. The filters used depend on the material tested and the end-use application. Different filter types allow for varying amounts of short-wave UV, which can significantly affect the speed and type of degradation. There are three commonly used filter categories, as defined by ASTM G155: Daylight, Window Glass and Extended UV. Figures 10-12 show the spectra that these filters produce. There are several types of Daylight, Window Glass and Extended UV filters. A complete explanation is available in the Choice of Filters technical bulletin, LX-5060. Also included is a close-up look at these spectra in the critical short-wave UV region from about 295 to 400 nm.
Test Specimen
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The Q-SUN Xe-1 table top model uses one xenon arc lamp.
The Q-SUN Xe-3 is a full size test chamber that has three xenon arc lamps.
The Q-SUN Xenon Test Chamber is available in both full size and table top models to accommodate your test specimens
The Q-SUN Xenon Test Chambers reproduce full-spectrum sunlight, which is filtered to eliminate unwanted wavelengths.
The Q-SUN chamber’s low-cost, air-cooled lamp and filters are easy to install and replace.
Figure 8 - Q-SUN Xe-3
Figure 9 - Q-SUN Xe-1
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Sunlight compared to the Q-SUN chamber with Daylight Filters. Daylight Filters are commonly used for simulations of outdoor exposure. They are an excellent reproduction of the full spectrum of natural sunlight, and are recommended for studies that value correlation to natural weathering.
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Sunlight through glass compared to the Q-SUN tester with Window Glass Filters. Designed for indoor light stability testing, this filter provides a spectrum that is essentially identical to sunlight through window glass. The spectrum is also useful for simulating general lighting conditions because it encompasses the same damaging wavelengths.
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Figure 10a - Daylight Filters and SunlightFull Spectrum
Figure 10b - Daylight Filters and SunlightUV Region
Figure 11a - Window Glass Filters and Sunlight Through Glass
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Figure 11b - Window Glass Filters and Sunlight Through Glass
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Sunlight compared to the Q-SUN xenon test chamber with Extended UV Filters. Certain automo-tive test methods require a spectrum that includes short-wave UV below the sunlight cutoff of 295. Q/B Filters produce that spectrum. Although they allow an unrealistic amount of short-wave UV, these filters often provide faster results.
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Figure 12a - Q/B Extended UV Filters and Sunlight Full Spectrum
Figure 12b - Q/B Extended UV Filters and Sunlight UV Region
Figure 13 - Q-SUN Xenon Test Chamber's SOLAR EYE Irradiance Control
Q-SUN Xenon Test Chamber cont.
Control of Irradiance. Xenon arc testers are typically equipped with an irradiance control sys-tem. The Q-SUN tester's SOLAR EYE system is illustrated in Figure 13.
Control of irradiance is especially important in a xenon tester, because xenon lamps are inherently less spectrally stable than fluorescent UV lamps. Figure 14 illustrates the difference in spectrum between a new lamp and a lamp that has been operated for 1500 hours. It is clear that, over time, the spectrum changes significantly in the longer wavelengths. However, when this same data is graphed as a percentage of change over time (Figure 15), it also becomes apparent that there is a similar shift in the short-wave UV portion of the spectrum. However, the controller does an excel-lent job at maintaining the spectrum at the 340 nm control point.
You can easily perform necessary calibrations with the CR20 Calibration Radiometer and CT202 Calibration Thermometer.
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Figure 14 - Xenon Lamps Spectral Output at 1500 Hours vs 0 Hours
Figure 15 - Xenon Lamps Spectral Output Over Time
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As xenon lamps age, the spectral output shifts in both the short and long wavelengths of light.
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After 1500 hours of use, xenon lamps change in spectral output, but the controller does a good job at maintaining the spectrum at the control point.
This change in spectrum due to aging is an inher-ent characteristic of xenon arc lamps. However, there are ways to compensate for this. For instance, lamps can be replaced on a more frequent basis to minimize the effects of lamp aging. Also, by using sensors that control irradiance at either 340 or 420 nm, the amount of spectral change in a particular area is minimized.
Despite the spectral shift from lamp aging, the xenon arc has proven to be a reliable and realistic light source for weatherability and light stability testing.
In addition to its other advantages, the patented SOLAR EYE system allows for easy calibration, NIST traceability and ISO compliance. Calibration radiometers and thermometers should be returned annually to Q-Lab's A2LA accredited lab for ISO 17025 compliant recalibration.
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Q-SUN Chamber's SOLAR EYE Irradiance ControllerThe Q-SUN tester is equipped with SOLAR EYE Irradiance Control, a patented, precision light control system. The SOLAR EYE allows the user to choose the desired level of irradiance. It automatically moni-tors and maintains the programmed light intensity. Irradiance is monitored and controlled at 340 nm, 420 nm or TUV.
Moisture Simulation. Most xenon arc testers simulate the effects of moisture through water spray and/or humidity control systems. The limitation of water spray is that when relatively cold water is sprayed onto a relatively hot test specimen, the specimen cools down. This may slow down the rate of degradation.2 However, water spray is very useful for simulating thermal shock and erosion. In a xenon arc, highly purified DI water is necessary to prevent water spotting.
Because humidity can affect the degradation type and rate of certain indoor products, such as many textiles and inks, control of relative humidity is recommended in many test specifications. The Q-SUN Xenon Test Chamber is available with optional relative humidity control.
Programmable water spray periods can operate dur-ing either the light or dark periods.
2 In competitive rotating drum type testers, relatively little water is used (about 3 seconds per 1 minute revolution). Because of the vertical specimen orientation, most of the water runs off the surface.
How it Works
Step 1: The operator selects the desired irradiance level (set point). The SOLAR EYE irradiance display shows the “Set” and “Actual” irradiance of the lamp.
Step 2: The built-in SOLAR EYE irradiance sensor measures the light intensity and transmits it to the controller.
Step 3: The SOLAR EYE Irradiance Controller compares the “Actual” measured irradiance to the “Set” irradiance point.
Step 4: The SOLAR EYE Controller adjusts power to the lamp to maintain the set-point irradiance.
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Practical ConsiderationsOf course, no matter how good the performance of a piece of testing equipment is, it will not be practical if it is too expensive to purchase or oper-ate. That is why purchase price, operating costs, and maintenance are critical issues and must be weighed against the benefits of owning a tester.
Purchase Price. In general, the QUV Accelerated Weathering Tester is more economical than a xenon arc chamber. For example, the Q-SUN Xenon Test Chamber may cost three times as much as the QUV tester, depending on the features and size of the unit.3
Capacity. Although the QUV/se model and the Q-SUN Xe-1 have a similar purchase price, they are very different in specimen capacity. The QUV has almost five times the speci-men capacity of the Q-SUN Xe-1, and near-ly 150% the capacity of the Q-SUN Xe-3.
Specimen Mounting. The QUV’s standard test sam-ple holders were designed for flat, relatively thin pan-els or specimens, although special specimen hold-ers are available for some limited types of 3-D parts. The Q-SUN tester allows more flexibility in terms of the types of specimens that can be mounted. It accommodates 3-D parts, test tubes and petri dishes, as well as flat panels.
3 Competitive rotating drum style xenon testers usually cost considerably more than the Q-SUN Xenon Test Chamber.
The Q-SUN Xe-3 accommodates 3-D parts, test tubes and petri dishes in addition to flat panels.
A QUV tester has five times the capacity of the Q-SUN Xe-1 and 1.5 times the capacity of the Xe-3.
The Q-SUN Xe-1 allows for versatile specimen mounting, including 3-D parts and flat panels.
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Ease of Use and Maintenance. Both the QUV and the Q-SUN testers are easy to use and easy to maintain. Both testers are completely automated and can operate continuously, 24 hours per day, 7 days per week. Automatic shutdown timers allow tests to finish at any time that is specified. Calibra-tion is also simple with the patented AUTO CAL system and calibration radiometers. Calibration is accomplished with a keystroke as the instru-ment automatically measures the lamp output and automatically adjusts the on-board control system accordingly. Test specimens and lamps all stay in place during the procedure.
The Q-SUN Xenon Test Chamber4 and the QUV Accelerated Weathering Tester are both designed to be user-friendly. Lamp loading and specimen mounting are simplified by the front access of the Q-SUN machine, and the double-sided access of the QUV tester.
Maintenance Costs. Both the QUV and Q-SUN machines offer relatively low maintenance costs. Q-SUN chamber annual lamp costs are significantly higher than the QUV/se or QUV/spray testers. Q-SUN tester electrical costs are also higher. Ad-ditionally, ordinary tap water can be used in the QUV/se and QUV/basic machines, whereas the Q-SUN chamber requires pure, de-ionized water. In summary, the QUV weathering tester's annual operating costs are considerably less than those of Q-SUN xenon test chamber.5
Q-SUN chamber lamp replacement is almost effortless: just open the hinged door, disconnect and slide out the lamp.
QUV/se model does not require lamp rotation. However, when the time comes to change a lamp, double sided access makes the job easy to perform.
4 Competitive xenon arc models that feature a water-cooled lamp and a rotating drum generally require significantly more maintenance than the Q-SUN Xenon Test Chamber. Calibration is more time consuming and cumbersome. Specimens are more difficult to mount, and the lamp/filter housing is much more complicated. 5 The Q-SUN chamber's maintenance costs, while higher than those of the QUV tester, are far less than those of competitive xenon arc testers. Q-SUN chamber lamps are considerably more economical than most xenon arc lamps, and Q-SUN chamber filters never need replacement. Electrical usage in a xenon arc can also be significant.
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Technical Summary: The Right Tester for the Right JobDeciding on the right weathering or light stability device can be confusing, especially if you are new to this type of testing. Which is the better for you? Below are some general guidelines. As with any generalization, there may be exceptions to the rule.
The QUV tester is better in the short-wave UV.
The QUV tester with UVA-340 lamps provides thebest available simulation of sunlight in the criticalshort-wave UV region. Short-wave UV typicallycauses polymer degradation in the form of glossloss, strength loss, yellowing, cracking, crazing,embrittlement, etc. In addition, the QUV machine’sfluorescent UV lamps are spectrally stable, with verylittle change in the SPD over time. This enhancesreproducibility and repeatability. For moreinformation, refer to the Choice of Lampstechnical bulletin, LU-8160.
The QUV tester is better at simulating the effectsof outdoor moisture.
The QUV machine’s condensation system (100%RH) is more aggressive and realistic than theQ-SUN’s water spray and humidity controlsystems. Deeply penetrating moisture may causedamage such as blistering in paints.
A Two Tier Approach. Because many researchers are concerned with all modes of polymer degradation, a two-tier testing programis often the best approach. Many manufacturers get cost-effective results by using the QUV AcceleratedWeathering Tester for physical property degradation and a Q-SUN Xenon Test Chamber for color degradation.
The Q-SUN chamber is a better match withsunlight in the long-wave UV and visiblespectrum.
Long-wave UV and even visible light can causepolymer degradation represented by color fade andcolor change for pigments and dyes. Wherecolor change is the issue, the Q-SUN chamber isusually recommended.
The Q-SUN tester, using Window Glass filters, isalso generally better than the QUV tester for testingindoor products. For more information, refer to theChoice of Filters technical bulletin, LX-5060.
The Q-SUN chamber is better for controllinghumidity.
The Q-SUN chamber can control relative humidity.This can be an important feature for humiditysensi-tive materials like many textiles and inks. Highhumidity can cause color shift and uneven dyeconcentrations.
LU-8009.4 © 2017 Q-Lab Corporation. All Rights Reserved.Q-Lab, the Q-Lab logo, QUV, Q-SUN, SOLAR EYE, AUTO CAL and CR10 are registered trademarks of Q-Lab Corporation.
Q-Lab Corporation www.q-lab.com
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